I bought the PWC portable 50GPD and it was a POS.
I should of just paid the more money up front for the 150GPD from Titanwaterpros that I have now.
Get a unit with clear canisters, with 300~ TDS the sediment filters would probably clog very quickly and you would be able to see it. I think I replaced the fitlers every 3 months when I was doing a lot of water changes for my s/w tank.
Getting clear canisters is not necessary imo. I purchased the cheap one on Ebay a while ago and I am still getting 0ppm. As long as you have a TDS meter, you don't need to visually inspect how dirty your filters are.
here is a review i started on mine:
Check out my new RO/DI unit